Abstract:
Integrated macro-, meso- and microstructural analysis of the part of the Michni area, located in the Mohmand Agency of NWFP, Pakistan, revealed at least five fabric- generating deformation events. The study area is characterized by a regional scale NNE-SSW trending synformal structure with moderately dipping pervasive foliation. Detailed microstructural analysis using Foliation Intersection/Inflection Axis technique (FIA) showed that the geometry of this regional fold postdates at least two bulk-shortening directions. The youngest FIA set 3 trends parallel to the axis of the synform, whereas FIA set 2 and I trend at high angle to the fold axis. Orientation of the FIA set 1 suggests early NNE-SSW shortening followed by NNW-SSE shortening. The trend of the FIA set 3 implies ESE-WNW bulk shortening. The orientation of FIA set 1 and 2 were obtained from inclusion trails preserved within the porphyroblasts. This suggests that the matrix foliation was the end product after extensive recycling of foliations, where the remains of early deformations were only preserved within the porphvroblasts. Unfolding of foliations using FIA technique has important implications to determine early bulk shortening directions, which is not possible by any other means. Moreover, the results of this study signify multiple shortening directions prior to or synchronous with the Himalayan orogenesis which were not reported previously.
Page(s):
9-22
DOI:
DOI not available
Published:
Journal: Geological bulletin (university of peshawar), Volume: 38, Issue: 0, Year: 2005